Effect of a successive feed of melt indole on the production of L-tryptophan by tryptophan synthase

A process of L-tryptophan (Trp) synthesis from indole (Ind) and L-serine by Escherichia coli transformant cells including tryptophan synthase was inve stigated. Usually, the reaction is strongly inhibited by Ind and Trp accumu lated. Therefore, we constructed a new system of successively feeding melt Ind into the reactor. Yield of Trp formation with this method was much larg er than that with a blanket feed of Ind. In a reactor of 1 L, a concentrati on of Trp formed = 92 g L-1 and an amount of Trp formation per amount of ce lls = 9.2 g(g-cell)(-1) were attained through 3-h reaction. The velocity of feeding Ind per amount of cells had the least upper bound in keeping Trp f ormation. Rate equations were constructed based on a model where the active enzyme was changed into an inactive one through the reaction. The hypothet ical equations successfully explained the reaction of Trp synthesis from In d and L-serine.